special report, a rare look inside the secret world of the kkk. For those of you who think burning crosses and hooded rallies are relative of the civil rights era, think again. Hate groups in america have doubled in the past decade and it may surprise you who is among their ranks and what their agenda is. Inside the new kkk. Forward, march. Reporter: In a forest grove not far from the nation's capital -- for god. For god. For country. For country. Reporter: A group of men and women gather. For race. For race. For klan. For klan. Reporter: And the lights fade, they enact a ritual over a century old, but is fresh and searing as the flame they ignite. Klansmen, the fiery cross. Reporter: A cross on fire. They. Reporter: Known as the invisible empire for a reason. They thrive in secrecy, almost never permitting outsiders access. Who are they? I could be your neighborhood. You don't know who I am. You could think the world of me, but yet if you see me in this hood, your thoughts could change. I been a fireman. I've been in the navy. Reporter:PEOPLE WEARING THESE Robes walk among us. If you want to be in the klan, fight for the klan. I fight for it seven days a week. Reporter: Witness the ku klux klan this summer -- white power. Reporter: In martinsville, virginia. White power! Reporter: And in tupelo, mississippi, a couple of weeks ago, a similar scene. White power! Reporter: Over the past four months, "nightline" has been granted rare access to the resurgent klan. Their rituals, their people, their message of racial segregation. We do not protect our race and protect our people, they gonna destroy it. They gonna kill us. Reporter: To get to the heart of it, we headed south to meet the grand dragon of the mississippi white knights of the kkk. Made infamous in the film "mississippi burning." You already been told once. Reporter: It's impossible not to think what once happened here. The territory scarred by the bomb ripped apart birmingham's 16th street baptist church, killing four children attending bible class. Reporter: So, we're in birmingham, alabama. And just down here is the jail where luther king jr. Wrote the famous letter from a birmingham jail. Along the way, we make a stop at the southern poverty law center, where mark potok and his colleagues have been fighting the kkk in courtrooms and classrooms for decades. Many of the klanspeople we've talked to say barack obama has been our single most effective recruiting tool in the last four, five years. Well, I think there's some truth to that. Immediately after obama was elected, we saw two of the largest hate websites in the country crash. Reporter: Potok told us that BY THE LATE '80s, THE KLAN Dwindled to a few hundred. They now number closer to 6,000. White power! Reporter: He believes they can be very dangerous. It's dangerous, not so much because a whole bunch of klansmen get together in a room and plan to murder 1,000 people with a bomb so, you know, it's the lone wolf characters that get frustrated with their leaders that break away, you know, one day, walk out of their house and start shooting. Reporter: With that in mind, at a gas station outside of tupelo, the grand dragon appears. He is also known as steven howard, 31 years old, he says he's an iraq war veteran. He comes with a loaded pistol on his hip and tells me he's got serious ptsd. We agree to follow him to a remote location, where cell phone service is spotty. Next to a trailer by the woods. They ask us not to photograph howard's 11-year-old daughter, but she is there, as is his wife, nicole, presiding over the food. Between eating and target practice -- I hit it that time. Reporter: There's work to be done. Howard and his klan brothers are preparing this 16-foot cross -- this is just -- we use the torches for the cross lighting itself. You have to wrap them and you have to put wire around them. Klansmen, behold the fiery cross. Reporter: When we come back, the burning cross that's terrorized people for generations. And the frightening message the klan is sending in the era of a black president. Barack obama don't care about us. He don't care about america.

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